1. Field of the Invention
The present invention generally relates to semiconductor devices and methods for producing semiconductor devices, and particularly, to a semiconductor device in which a semiconductor chip (element) is bonded to a plurality of leads by wire-bonding and a method for producing such semiconductor devices.
Recently, semiconductor chips have been highly integrated and the method for producing the semiconductor chips comprises steps which require extremely fine operations. Also, according to progress in the semiconductor industry, semiconductor devices having high power have been developed. Naturally, this results in an increase in the amount of heat generated by the semiconductor devices and some semiconductor devices have a structure in which a heat spreader (heat dissipating plate) is provided in order to improve its heat dissipating ability.
On the other hand, there are demands for a semiconductor having high reliability which may be produced at a low cost. Hence, the development of a semiconductor device having properties which may respond to such various requirements is awaited.
2. Description of the Related Art
A conventional semiconductor device will be explained with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing a cross-sectional view of a conventional semiconductor device 1 and FIG. 2 is a diagram showing a region of a wiring position of a semiconductor chip (element) 2 shown in FIG. 1 in a magnified scale.
As shown in FIG. 1, the semiconductor device 1 is comprised of the semiconductor chip 2, a plurality of leads 3, a heat spreader (heat dissipating plate) 4, a plurality of wires 5, adhesive tapes 6, and sealing resin (resin package) 7. The numeral 9 indicates an adhesive composition.
The semiconductor chip 2 shown in FIG. 2 is a so-called bare chip and a plurality of pads 8 are provided on the semiconductor chip 2. As mentioned above, since high integration and high power are required for the semiconductor device 1, there is a tendency to increase the number of pins formed on the semiconductor chip 2 and, accordingly, the pitch, P, shown in FIG. 2 of the pad 3 tends to be decreased.
Also, the number of leads 3 corresponds to the number of pads 8 provided with the semiconductor chip 2, and hence the number of leads 3 tends to increase. As shown in the figures, an inner lead portion 3a of the lead 3 is connected to the corresponding pad 8, which is provided with the semiconductor chip 2 by the wire 5, and an outer lead portion 3b of the lead 3, which is formed in a gullwing shape in order to make a surface mounting of the semiconductor device 1 possible, extends outside of the sealing resin 7.
The heat spreader 4 may be made of a flat-shape member having an excellent thermal conductivity and the semiconductor chip 2 is adhered to substantially the center thereof using the adhesive composition 9. Also, the inner lead portion 3a of the lead 3 is connected to the heat spreader 4 using the adhesive tape 6 which has a structure in which an adhesive composition is applied to an insulative resin film. Moreover, the sealing resin 7 is formed so as to cover at least the semiconductor chip 2 and the wire 5, and it may be formed using a technique such as a mold technique.
In the above-mentioned configuration of the semiconductor device 1, the reasons that the inner lead portion 3a is connected to the heat spreader 4 using the adhesive tape 6 are as follows.
When the wire 5 is provided between the inner lead portion 3a of the lead 3 and the corresponding pad 8 provided on the semiconductor chip 2, the above-mentioned wire-bonding is carried out and, in general, an ultrasonic bonding method is used for the wire-bonding process. On the other hand, the number of pins used has increased these days and the pitch, P, between each of the pads 3 is reduced, the area of the end portion of the inner lead portion 3a (i.e., the bonding position for the wire 5) is reduced accordingly and its mechanical strength is also decreased.
Therefore, if the wire-bonding is performed such that a space is present between the inner lead portion 3a and the heat spreader 4 (i.e., so-called space bonding), the lead 3 and the heat spreader 4 tend to contact each other and there is a danger that an electrical short is caused among a plurality of leads 3 since the heat spreader 4 is generally made of a metal having excellent thermal conductivity. For this reason, the inner lead portion 3a is connected to the heat spreader 4 using the adhesive tape 6 in order to achieve an insulation of the inner lead portion 3a and the heat spreader 4 as well as increase the mechanical strength of the inner lead portion 3a.
However, in the conventional semiconductor device having a structure in which the inner lead portion 3a is connected to the heat spreader 4 using the adhesive composition 6, there is a danger that gases are generated from the adhesive tape 6 during a cure (heat) process which is carried out after the inner lead portion 3a is connected to the heat spreader 4 and the inner lead portion 3a is damaged (corroded, for instance) by the generated gases.
In order to avoid the above problem, the lead 3 may be subjected to a washing process such as a plasma cleaning process before carrying out a wire-bonding process. However, this makes the manufacturing process of the semiconductor device complicated and the cost for producing the semiconductor device is increased.
Also, if the area of the adhesive tape 6 is reduced in order to avoid the problem, it is likely that the inner lead portion 3a is bonded to the heat spreader 4 in a state that they are not in contact with each other (i.e., the space bonding), and the electrical short may be caused among a plurality of the leads 3 which, as a result, reduces a reliability as well as yield of the semiconductor device.